Repair of vitreous enamelware equipment



Patented Aug. 8, 1944 2,355,414 mama or vrraaous ENAMELWABE EQUIPMENT Spencer Walsh Shepard, Warren Township. 8cm. erset County, and John Stanley Mag'lelnlcki, South River, N. J., minors to American Cyanamid Company, New York, N. Y., a corporation of Maine No Drawing. Application April 9, 1943, Serial No. 482,508

3 Claims.

This invention relates to an improvement in the repair of enamel and glass-lined chemical equipment.

Many chemical operations involve the use of materials which are highly corrosive to metals. It is customary in such processes to utilize equipment made of metal, frequently steel, which has been coated with a vitreous enamel or with glass. During the cours of use it happens sometimes that the glass or enamel coating is broken and 'such breaks are very serious'matters because even a small break-will permit corrosive reaction mixture to-reach the underlying metal, corrode it, and rapidly spread the break.- In the past four methods have been in general use. The first is to form a small gold plug in the break by tamping in gold leaf. The gold forms a satisfactory repair so long as it sticks, but is open to very serious disadvantages. In the first place it can only be used for very small breaks. Its adhesion to the enamel and metal is poor, and the process is relatively slow. A second process is a so-called cold patch with various acid proof cements and protective coatings. This method permits patching larger breaks, but does not produce as chemically resistant a repair, nor does it give good adhesion. The third method is to re-enamel or reline the equipment. This, of course, produces a perfect repair, as it puts the apparatus into its original condition, but it cannot be effected in situ and is very costly and time-consuming. The fourth method is to bake on various organic resins of the thermosetting type. This method has a disadvantage that there is a tendency for the resin to spall oil and the resistance of the resin is not proof against all corrosive liquids.

Th present 'inventionproduces a repair to breaks in enamel or glass-lined equipment which is not subject to the disadvantages of the prior methods. Essentially the present invention is a combination of three steps which must be used together and which, while not per se new mechanlcal procedures, have never been used together in the repair of enamel or glass-lined equipment, and when so used produce a new and vastly improved result. The first step is a preparation of the surface of the break by means of sand or grit blasting in order to roughen th surface. Then a coating, preferably a metallic coating such as a noble metal, is sprayed on with a metalllzing gun, that is to say a device in which the metal is sprayed through a flame so that it strikes the surface in the form of minute molten or semi-molten droplets. The metallic coating is then preferably smoothed with a wire brush and then is coated with an organic resin, preferably in several coats with intermediate brushing or'buiiing in order to assure good adhesion.

The process ol'the present invention possesses the important advantages that the three steps are not particularly expensive, can be carried out without removing the equipment from its location, and a repair is obtained which is far superior to gold plugs, cold patching, or baked enamel, and it, of course, involves but a minute fraction of the cost of re-enamelling. The advantages over the gold plug method are that the present process is not limited to small breaks and can be used on breaks of any size or shape. An excellent adhesion of the sprayed material is obtained, both to metal and enamel. and the process is much more rapid than tamping in gold. The present invention represents an im portant advantage over cold patching in that it produces a completely chemically resistant patch which lasts practically indefinitely. There is no diflicuity involved in spelling as in the case of baked-on organic resin and coatings and the patches produced when using suitable material are superior in their chemical resistance.

It is an important advantage of the present invention that good adhesion is obtained regardless of th shape, wherever the break in the enamel or glass coating extends through to the underlying metal, and it is possible not only to patch breaks in relatively flat surfaces, but also on sharply curved surfaces, such' as stirrers and the like.

It is a further advantage of the present invention that it may be used with a wide variety of materials which can be sprayed on with a so-called metalllzing gun. Extremely successful results are obtained with various grades of gold from 18 carat to 24 carat. Less pure gold may be used where the corrosion requirements permit, and fine silver is also readily applied and is suitable where the corrosion resistance of silver is adequate. In certain specific cases organic materials may be sprayed on with a metal- The resin coating over the repair may use any suitable material such as a synthetic drying oil coating comprising a divinylacctylene poly mer. Thermo-setting phenol formaldehyde lacquers are also suitable.

The last step of the process of the present invention, namely th coating with a corrosion resistant lacquer, is of importance in protecting the metal mechanically. Under favorable conditions, where the material sprayed on with the Example 1 The area around the break in the enamel of a piece of enamel-lined equipment is masked off with cellulose tape and the area of the break subjected to grit blasting using a commercially available silicon carbide abrasive of i mesh. The blasting is efiected with an air pressure of 80-95 lbs. Blasting of the broken area is continued until the metal base presents a coarse matte appearance. The tape surrounding the break is then removed and the sound enamel lightly blasted for about /2 to inch around the break.

Metallizing is then effected using a wire gun and 18 gage 18 carat gold wire. The gun is provided with an 18 gage nozzle and air cap and uses oxygen, acetylene, and compressed air. The

oxygen is under a pressure of some 16-18 lbs.,

the acetylene from 17-19 lbs.,a'nd the air 60-75 lbs. The metallizing gun is used in a normal manner and may be held at a distance of about 6 in. from the work, except where there may be deep pits or cavities, where the gun should be held closer to the work in order to build them up. If the surface break is large it is desirable to feather out the spray along the edges by removing the gun to a distance of about 8 in., so as to obtain better adherence to the enamel.

After metallizing is complete the deposit of metal is brushed with a soft wire brush from the center out to the edges in order to overcome porosity. The repair is then coated with seven coats of a synthetic drying oil, such as that sold by the du Pont Company under designation 8. D. O. The first two coats are thoroughly wire-brushed over the metal patch in order to fill in any pores in the metal.

Example 2 The procedure of Example 1 is followed except that fine silver wire is used in place of the gold wire. The patch produced gives complete protection within the corrosion limits of silver.

Example 3 The procedure of Example 1 is followed except that 24 carat gold is used and a very coarse spray is obtained by reducing oxygen pressure to 6 lbs., acetylene to 7 lbs., and air to 35 lbs., or if desired by omitting the oxygen entirely. This coarse spray is poorly atomized and the metal appears to be deposited in the form of molten droplets. With the soft gold, however, good adhesion is obtained and a sound patch produced.

We claim:

1. A method of repairing breaks in the vitreous lining of steel equipment lined with vitreous ma terial, which comprises producing a clean roughened surface extending through to the metal by abrasive blasting and applying a coating of precious metal by means of a metallizing gun.

2. A method of repairing breaks in the vitreous lining of steel equipment lined with vitreous material, which comprises producing a clean roughened surface extending through to the metal by abrasive blasting and applying a coating of a member of the group consisting of gold and gold alloys by means of a metaliizing gun and coating the resultant repair with an adherent continuous coating of a corrosion resisting filmforming organic material capable of resisting elevated temperatures.

3. A method of repairing breaks in the vitreous lining of steel equipment lined with vitreous material, which comprises producing a clean roughened surface extending through to the metal by abrasive blasting and applying a coating of fine silver by means of a metallizing gun and coating the resultant repair with an adherent continuous coating of a corrosion resisting film-forming organic material capable of resisting elevated temperatures.

SPENCER WALSH SHEPARD. JOHN STANLEY MAGIELNICKI. 

